In asynchronous communication systems data is normally received and reconfigured into machine language which is a hexa-decimal representation of an alphanumeric character. This hexa-decimal character is then stored in a text storage buffer that will accumulate these characters until a software routine, called a display access method, can process them into a sufficient format for display on a cathode ray tube. The last step in the display access method will update the display with the new data.
The display access method typically takes an average of 30 milliseconds to process a given set of characters stored in the text buffer. For low transmission rates such as 110 bits per second, a new character, which normally consists of 10 or 11 bits, is received about once every 100 milliseconds. Since the display processing software only requires 30 milliseconds to register the character on the display, there remains 70 milliseconds available for additional work such as background print.
However, at a transmission rate of 1200 bits per second, a new character, which normally consists of 9 bits but may be 10 bits, occurs every 7.5 milliseconds. During each cycle of the display access method, approximately four characters will be received and stored in the receive buffer. At the end of the display access method cycle the system will recognize that new data is available in the receive buffer and this data will be transferred to the text storage buffer and the display access method will be initiated. This requires the display access method to continuously recycle consuming virtually 100% of the software overhead trying to keep the screen updated with new data.